1. Field of the Invention
This invention relates to a mechanism for controllably advancing a rotating cylindrical member and, more particularly, to a sealing structure that prevents migration of foreign matter between relatively movable parts on the mechanism.
2. Background Art
It is well known to use multiple advancing rollers to controllably convey a rotating, cylindrical member, such as a sewer cable. Exemplary mechanisms are shown in each of U.S. Pat. Nos. 3,394,599, 3,451,090, and 5,239,724. In each mechanism, a plurality of advancing rollers surround and are abutted to a rotating cable. With the rotational axes for the advancing rollers parallel to the length of the cable, the system is in a neutral or idling state. The rollers are simultaneously repositionable to cause the roller axes to align transversely to the lengthwise axis of the cable. The canted rollers acting on the outer surface of the rotating cable effect advancement thereof in a direction and at a rate determined by the angle between the roller axes and the cable length.
Each of the advancing rollers is mounted to a carrier which is moved in a passage defined by a mounting block. The passage is bounded by a surface which guides the carrier both in rotation about the center axis of the passage and in translation axially of the passage.
In operation, the rollers contact the outer surface of the rotating cable and thereby tend to dislodge foreign matter therefrom. This foreign matter, in the form of grime and particulate, tends to find its way into the passage between the carrier and the inner block surface. Ultimately, the accumulation of foreign matter within the passage may inhibit canting of the rollers through rotation of the carriers. In an extreme case, the carriers may lock up in the blocks.
It is known to provide a grease fitting on the mounting block and to introduce grease under pressure into the passageway so as to squeeze particulate and grime outwardly oppositely to the direction in which it gained entry. In so doing, the carrier becomes lubricated to allow freedom of movement.
One problem with this conventional system is that it is virtually impossible to control the incoming grease so that it fully flushes the grime and particulate away from the passageway. Instead, some of the lubricant commonly causes the particulate and grime to move oppositely to the desired direction and lodge in bearings in the passage at the closed axial ends thereof. Needle bearings, which are commonly used at the closed end of the passage to guide rotation of the carriers, are prone to locking up when exposed to this type of foreign material.
Further, it is an inconvenience to have to periodically maintain the unit by introducing grease. If maintenance is postponed, damage to the unit, i.e., the needle bearings, might occur, necessitating replacement thereof.
As an alternative to introducing grease, it is also known to disassemble the carrier and block assembly to facilitate cleaning thereof. This is highly inconvenient, particularly when this cleaning must take place in the field.